This invention relates generally to pressure operated relief valves and more particularly concerned a novel two-stage pilot valve, providing pressure operation of a relief valve having substantially larger capacity. In particular, the valve disclosed provides improved main valve operation through control of pressure dynamics of the combination pilot, main valve, and associated pressure conduit or vessel. An improved method of calibrating and testing pressure sensitive elements is also provided.
Prior art relief and/or valve combinations are disclosed in U.S. Pat. Nos. 3,595,263, 3,664,362, 3,512,560 and 3,568,706. However, the operation provided by these combinations of main and pilot valves do not adequately provide for control of the dynamic relationships between the pilot valve, main valve, and pressure vessel or conduit. In addition, the prior art valves in many cases, when tested on site, provide a method of testing only a pilot valve set point. The reset or blowdown pressure setting of the pilot valve first stage operation remain untested. Testing and/or calibration checking by operation of the entire unit through increased pressure of the associated vessel or tank, necessitates release of the stored tank or vessel product which in many cases is highly undesirable. The unit disclosed here provides for onsight testing of both major elements of the relief system, and main valve, or alternately the pilot valve first stage alone. Therefore, it is an object of the invention to provide a two-stage pilot valve for operation of a larger capacity pressure relief valve wherein test operation of the first stage pilot is possible without raising main valve pressure.
It is an object of the invention to provide a pressure relief valve of substantial capacity having improved control of the flow and pressure dynamics associated with the relief valve and pressure vessels or conduits requiring pressure relief.
It is a further object of the invention to provide a unique two-stage pressure sensitive pilot valve, wherein flow of the pressurized product through the valve occurs only during the transient, or transitional stage.
It is a still further object of the invention to provide a two-stage pressure operated pilot valve for operating main relief valves of substantially larger capacity wherein the pilot flow can be highly filtered providing increased reliability to freedom from contamination.
It is an additional object of this invention to provide a pilot operated relief valve for operation at medium to high pressures wherein the dynamic relationship between the calibrated first stage and flow amplifying second stage has a substantial range of adjustment, providing adequate transient free operation of the associated main valve over a wider range of piping and pressure vessel configurations.